DESCRIPTION: In the broadest sense, Dr. Feher's objective is to understand biological processes and phenomena in terms of physical mechanisms; i.e., on a molecular level. The main problem addressed in this proposal deals with the conversion of electromagnetic energy into chemical energy; i.e., photosynthesis. This is one of the most basic processes in biology; all energy of the living world is derived from it. At the heart of the photosynthetic process is a membrane bound protein-pigment complex called the reaction center (RC). Dr. Feher studies the structure and function of the RC and the secondary donor, cytochrome c2. The mechanisms of electron and proton transfers that take place in the RC are of general interest and importance in all living systems. For instance, the processes that occur in mitochondria (e.g. in mammalian cells) can be viewed as the reverse process of photosynthesis utilizing similar mechanisms. Furthermore, the RC, being the best characterized membrane bound protein, serves as an excellent model for other membrane proteins that perform important functions in a variety of biochemical processes. The necessity of having single crystals to determine structures led Dr. Feher to a basic investigation of the crystallization mechanisms of macromolecules. Crystallization, in addition to being of great practical importance, serves as an example of molecular association (recognition); a ubiquitous phenomenon throughout the living world. The fields and methodologies involved in this work are interdisciplinary, ranging from physics to chemistry and molecular biology. The techniques used are: X-ray crystallography, electron and atomic force microscopy, optical and magnetic (EPR/ENDOR) spectroscopy, computational (e.g. Monte Carlo simulations), protein chemistry and recombinant DNA techniques. The specific problems addressed are: The three-dimensional structure of native and mutant RCs from the photosynthetic bacterium Rb. sphaeroides, the structures of cytochrome c2, the RC-cyt c2 complex, the RC from photosystem II of green plants; electron transfers in RCs, calculation of electrostatic energies in RCs and the mechanism of crystallization of biological macromolecules.